Importance

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Abstract

A hydraulic neutral cold start control valve for a variable displacement hydraulic unit includes a housing with a spool bore and an intersecting signal pressure passage therein. A spool is disposed in the bore and is mechanically biased to a closed or neutral position of the valve by a pair of opposing springs. A plunger is associated with one of the springs and has a surface that usually sealingly contacts one end of the spool but extends radially therebeyond such that it is in fluid communication with the signal pressure passage. When the signal pressure exceeds a threshold value, the pressure forces the plunger to separate from the end of the spool. Then the movement of the spool becomes proportional to the signal pressure, which is desirable for normal operation and control of the hydraulic unit. If the vehicle powering the hydraulic unit is shut off or the signal pressure is interrupted such that it drops below the threshold value, the opposing springs resume control and move the spool to a neutral position. This ensures that low torque will be required to restart the vehicle, even under cold oil conditions.

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First Claim